Electromagnetic sound-producing device



F. J. AND W L. KAEHNI.

ELECTROMAGNETIC SOUND PRODUCING DEV ICE.

APPLICATION FILED JUNE 9.1922.

1,426,743. Patented Aug. 22, 1922.

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IPATENT @FFEQE.

FRANK J KAEHNI AND NEEDLIAM L. KAEHNI, OF CLEVELAND, OHIO.

ELECTRQMAGNETIC SOUND-PRODUCING DEVIGE.

Specification of Letters Patent.

Patented Aug. 22, 11922.

Application filed June 9, 1922. Serial No. 567,042.

T 0 all whom it may concern:

Be it knownthat we, FRANK J. KAEHNI and W ILLIAM L. l AEHNI, citizens ofthe United States, residing at Cleveland, in the county of Cuyahoga andState of Ohio, have invented a certain new and useful Improvement inElectromagnetic Sound-Producing Devices, of which the following 15 afull, clear, and exact description, reference being had to theaccompanying drawings The object of this invention is to provide averysimple electro-magnetic device for producing a comparatively largevolume of sound corresponding in its rate of vibration to variations inthe electric current through the device. Our sound producer has a v1-bratory magnetic member controlled by a coil and adapted to coact with aneedle of a reproducing diaphragm as used in a phono raph.

ur vibrating device has a special use in radio telephony, and is welladapted to enable the current variations so caused to operate thereproducer of a standard phonograph and thus utilize such reproducer andthe horn and sound chamber of the phonograph as a loud speaker. Ourdeviceis very simple and compact and may read ly stand on a phonographtable ad acent the rotating disc in position to be engaged by 'theneedle of the reproducer without any change whatsoever in the phonographmech anism.

Uurinventio is illustrated in the drawings hereof an is hereinafter morefully described and its essential features are summarized in the claims.

In the drawings, Fig. 1 is a plan of our sound producing device, andF1g. 2 1s a side elevation thereof, the casing in each case being shownin section; Fig. 3 is a central vertical section transversely of thedevice; Fig. 4 is a plan of a phonograph showin our device in positionthereon; and Fig. 5 1s a diagram illustrative of the operation.

Referring first to Fig. 5, 10 indicates a horseshoe magnet, shown asan'electromagnet energized by coils 20 connected with a suitable batteryindicated by A. 30 ind cates a bar of magnetic material which 1s fixedlymounted at one end and has its other end free and adapted to vibratebecoil in the oposite direction produces a reverse movement. Thus, avibration is given to the bar 30 dependent on the current vanations inthe circuit through the coil 40, and if the phonograph needle is restingon the upper end of the bar, such vibrations will be transmitted to theneedle and thence to the diaphragm, producing sound vibrations in thehorn and sound chamber. The upper end of the bar 30 has a smalldepression 38 adapted to receive the point of the phonograph needle.

Figs. 1 to 4 illustrate our device specifically embodied with referenceto use in a phonograph. In these views. the horseshoe magnet consists ofa suitable base 11 and two L-shaped arms 12 tightly secured thereto,asby screws 14. The vibrator bar 30 is secured to the mid-point of thecore base 11. It has preferably a reduced shank 31 to enable its moreready vibration, an enlarged collar 32 below such shank, which isadapted to rest on the top of the base 11, and a screw-threaded stud 33extending into the base; This-stud receives a nut 35 for tightly holdingthe bar on the base member of the magnet.

The end portions of the magnet core are preferably narrowed and extendto the opposite sides of the vibrator bar, as shown at 15 in Fig. 1.Thus this bar being alternately repelled and attracted by each polepiece is caused to vibrate in a plane transverse to the general plane ofthe magnet core 10. Each of these end portions 15 carries an iron screw16 threaded in the portion 15 and locked by a jamb nut 17. These screwsform the ultimate pole pieces of the horseshoe magnet and by reason oftheir adjustment enable these pole pieces to stand equidistant from thebar 30 when the normal direct current from the B battery is flowingthrough the coil 40, or where there is normally no current.

wound on a hollow headed spool 41 through the bore of which the bar 30loosely extends. As shown, the lower head of the coil 40 is extended toprovide ears 42 for securing it in place, and suitable screws 43 pass,through' these ears and through distance blocks 44 into a suitablebase.

The device mentioned is mounted on a suitable base, as for instance awooden block 50 which as shown is recessed to receive the magnet base11. It also receives the screws 43 which hold the coil 40 in place. 52indicates a suitable casing which houses the various parts mentioned andmay rest on a shoulder 51 of the base.

bar 30 extends. The casing is preferably depressed about the opening asshown at 54, so that the bar will not extend beyond the casing andhencewill not be liable to displacement. K

The base 50 may readily extend at one side of the casing and be thereprovided with binding posts for the different circuits or other terminalarrangements may be made as desired. We have shown four binding posts61, 62, 63, and 64 mounted on such extended portion of the base; theposts 61 and 64 forming terminals of the coils 20 (which are connectedby a conductor 65), and the posts 62 and 63 forming the terminals of thecoil 40.

In Fig. 4, 70 designates the table of a phonograph, 71 the rotatingdisc, 72 the sound arm, 73 the reproducer box thereof, and 74, Fig. 2,the needle of the reproducer. It will be noted that our magnetic devicestands parallel to the general plane of the reproducer diaphragm andbox, and the needle is thus vibrated in its normal direction, as whencontacting with a record disc.

When our device is connected for use, the current from the battery A(which may be the usual six volt A-battery used in radio work) energizesthe coils 20, and the audion may be connected with the coil 40 so thatthe current from the usual B battery in. the plate circuit flows throughthis coil.

Theresult is that the upperend of the bar 30 becomes a north or southpole of a certain intensity and thus moves a slight distance toward thesouth or north pole of the horseshoe magnet. The screws 16 having beenadjusted so that the bar stands substantially mid-way of their ends whenthe B battery is on, the device is ready for use. the current from the Bbattery is varied This casing has an opening 53 in its top through whichthe Now, if

by reason of variation in potential of the grid of the audion, thecurrent through the coil 40 will be either strengthened or weakened. Ifstrengthened, the bar 30 becomes a stronger pole than it was before andhence moves further toward the screw 16 of opposite polarity, while ifthe grid potential weakens theflow of current from the B battery, thebar 30 becomes a weaker pole than it was and moves in the oppositedirection. We accordingly have vibrations of the bar 30 ataudio-frequency corresponding to thevariations in potential at the gridof the audion, and thus audio-frequency vibrations are transmitteddirectly to the phonograph needle causing sound from the sound arm andsound chamber.

If our device is coupled in the secondary circuit of an audio-frequencytransformer, so that there is no direct current through the coil 40, theupper end of-the vibrator will normally be neutral and will stand in midposition between the poles of the horseshoe magnet, but with analternating current input will become alternately a north and a southpole, according to the direction of current, The result will be avibration the same as already described.

The vibrations of the bar 30 are very slight, so slight as to beunobservable to the naked eye, though they may be detected by touch.Experience has demonstrated that they operate to give the needle thesame kind of vibration which is received from an ordinarydisc record andhence corresponding sound is produced. We have found that the mechanicalresistance of the bar 30- and its inertia have a desirable effect inpreventing extreme vibrations and reducing undesirable sounds caused bystatic electricity. We have accordingly been able to produce verysatisfactory reproductions with this device.

Claims to the broader combination of a magnetic device actuating aphonograph remagnetized armature connected to the phonograph reproducerneedle.

We claim 1. The combination with a phonograph reproducer having arockable stylus, a sound box, and a sound reproducing diaphragm, of amagnetic core having a pair of end portions adjacent each otheroverlapping and spaced apart, iron screws adjustably mount ed in saidend portions. and forming pole pieces, a bar rigidly anchored at itslower end to the intermediate portion of the magnetic core and extendingupwardly between said pole pieces and adapted to vibrate transversely tothe general plane of the mag net core and having means at its upper endfor connection to said phonograph stylus, a

coil. surrounding said bar and spaced therefrom, and a casingsurrounding the magnet and coil and having an opening adjacent the endof said bar.

2. The combination with a phonograph reproducing device comprising asound box,

a rockable stylus carried by the sound box,

a sound reproducing diaphragm actuated by said stylus, of a base, ahorseshoe magnetic core carried thereby having its'end portions adjacenteach other and overlapping and spaced apart, energizing coils on the twolegs of the core respectively, an iron bar anchored at its lower end tothe intermediate portion of the magnetic core and extending upwardlybetween said pole pieces and having a depression in its upper end forour signatures.

FRANK J. KAEHNI. \VILLIAM L. KAEHNI.

